This invention is concerned with shaped bodies of plastic material having a high elasticity and high adhesive characteristics. Said shaped bodies, like e.g. foils, can be firmly adhered to a substrate, like e.g. a silicon containing substrate, due to their good adhesion. Said shaped bodies contain high quantities of a benzophenonetetracarboxylic acid tetraester as a elastifying component, usually 15-90 parts by weight of said elastifying component per 10 parts by weight of the plastic material. The highly elastic shaped bodies can e.g. be ion selective membranes which contain as further component an ion selective substance.